Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07K—PEPTIDES
  • C07K14/00—Peptides having more than 20 amino acids; Gastrins; Somatostatins; Melanotropins; Derivatives thereof
  • C07K14/435—Peptides having more than 20 amino acids; Gastrins; Somatostatins; Melanotropins; Derivatives thereof from animals; from humans
  • C07K14/78—Connective tissue peptides, e.g. collagen, elastin, laminin, fibronectin, vitronectin or cold insoluble globulin [CIG]
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
  • A61K38/00—Medicinal preparations containing peptides

Definitions

• BACKGROUND Collagen is the most abundant protein in vertebrates, occurring in virtually every tissue, including skin, tendon, bone, blood vessel, cartilage, ligament, and teeth.
• Collagen serves as the fundamental structural protein for vertebrate tissues. Collagen abnormalities are associated with a wide variety of human diseases, including arthritis, rheumatism, brittle bones, atherosclerosis, cirrhosis, and eye cataracts. Collagen is also critically important in wound healing. Increased understanding of the structure of collagen, and of how its structure affects its stability, facilitates the development of new treatments for collagen-related diseases and improved wound healing treatments.
• Collagen is a fibrous protein that can exist in a variety of related forms. Mammals produce at least 17 distinct polypeptide chains that combine to form at least 10 variants of collagen. In each of these variants, the polypeptide chains of collagen are composed of approximately 300 repeats of the sequence X-Y-Gly, where X is often a proline (Pro) residue and Y is often a 4(R)-hydroxyproline (Hyp) residue.
• Connective tissue such as bone, tendon, cartilage, ligament, skin, blood vessels, and teeth
• individual collagen molecules are wound together in tight triple helices. These helices are organized into fibrils of great tensile strength, Jones & Miller, ). Mol. BioL, 218:209- 219 (1991 ). Varying the arrangements and cross linking of the collagen fibrils enables vertebrates to support stress in one-dimension (tendons), two-dimensions (skin), or three- dimensions (cartilage).
• the collagen polypeptide is translated with the typical repeat motif being ProProGly. Subsequently, in vivo, the hydroxylation of Pro residues is performed enzymatically after collagen biosynthesis but before the chains begin to form a triple helix. Thus, hydroxylation could be important for both collagen folding and collagen stability.
• the hydroxyl group of Hyp residues has long been known to increase the thermal stability of triple-helical collagen, Berg and Prockop, Biochem. Biophys. Res. Comm., 52:1 15-120 (1973). For example, the melting temperature of a triple helix of (ProHypGly) 10 chains is 58° C, while that of a triple helix of (ProProGly) 10 chains is only
• a better understanding of how the structure of collagen contributes to its stability would facilitate the design of a collagen or collagen mimics having improved stability.
• a high stability collagen substitute could advance the development of improved wound healing treatments.
• Tissue welding is a wound healing technique in which a laser is used to thermally denature the collagen in the skin at the periphery of a wound.
• the wound is reannealed by permitting the renaturation of the collagen.
• a "filler" or solder is required to effect reannealing of the wound.
• Various materials, including human albumin, have been used as solders for this purpose.
• a good solder is resilient and is non-immunogenic and should preferably be capable of interaction with native collagen in adjacent sites.
• Collagen is also used for a variety of other medical purposes.
• collagen is used in sutures which can be naturally degraded by the human body and thus do not have to be removed following recovery.
• a sometimes limiting factor in the design of collagen sutures is the strength of the collagen fibers.
• a collagen variant or mimic having a greater strength would aid in the usage of such collagen sutures by relieving this limitation.
• Fluoroproline (Flp) was synthesized by Gottleib et al., Biochemistry, 4:1 1 :2507-
• Gottleib et al. claimed to have incorporated both isomers into collagen by a biosynthetic route, but that claim was later refuted by Takeuchi et al., Biochem. Biophys. Ada, 1 75:156-164 (1969), Takeuchi and Prockop, Biochem. Biophys. Ada, 1 75:142-155 (1969), and Uitto and Prockop, Arch. Biochem. Biophys., 181 :293-299 (1977). Because Gottleib et al. used biosynthesis, to the extent that Flp was incorporated at all into the resulting collagen molecules, it would have been incorporated randomly into the polypeptide in place of some random proline residues.
• the present invention is summarized in that a novel variant of collagen has been designed which forms a stronger triple helix than does native collagen.
• the novel variant includes a fluorinated proline residue substituted for the hydroxyproline residue characteristic of the triple repeats normally found in native collagen.
• Fig. 1 shows the circular dichroism spectra of (Pro-Flp-Gly) 10 , (ProProGly) 10 , and (ProHypGly) 10 .
• Fig. 2 illustrates the synthetic route for the production of FmocProFlpGlyOH, as described in the examples below.
• Fig. 3 illustrates the synthetic route for the production of (ProFlpGly) 10 , as described in the examples below.
• the Hyp residues ⁇ r ⁇ crystalline collagen do not have unusual ⁇ or ⁇ bond angles. But, 03 angles (which are the dihedral angles of the peptide bond) merit consideration.
• all of the peptide bonds in triple-helical collagen are in the trans conformation. This leads to the hypothesis that Hyp residues could favor the trans conformation.
• the collagen mimic (Xaa-Flp-Gly) 10 was synthesized, where Flp is 4(R)-fluoro-L-proline, as described in detail in the examples below.
• Flp residues the fluorine atom imposes a strong inductive effect, but does not form hydrogen bonds.
• the thermal stabilities and helicity of (ProFlpGly) 10 (ProProGly) 10 , and (ProHypGly) 10 were determined using circular dichroism.
• the collagen mimic (ProFlpGly) 10 was found to form a very stable triple helical collagen, stronger than either of the other forms tested.
• collagen mimic (ProFlpGly) 10 is useful as a collagen mimic for making collagen compatible materials, but that the critical parameter in the formation of the collagen triple helix structure is the inductive effect on electron density at the 4 position in the proline in the middle position of the triple repeat motif.
• Forms of collagen mimics having other amino acids at the first position in the triple motif is contemplated here.
• the present invention is a collagen mimic comprising a triple repeat motif peptide having the formula (XaaFlpGly)n, where Flp is 4(R)-fluoro-L-proline, n is a positive integer, and Xaa is any amino acid, but is typically one of the 20 naturally occurring amino acids.
• the collagen mimics that were synthesized and tested had a proline residue at position Xaa. It is anticipated that amino acids other than proline would be tolerated in the Xaa position, given that natural collagen has a wide variety of amino acids in the Xaa position, although proline would be the prototypical residue at that position.
• the residues in the Xaa position can be the same or can vary in identity along a single molecule.
• the examples below describe the chemical synthesis of a collagen having the sequence (XaaFlpGly)n.
• the present invention is intended to encompass a molecule comprising the sequence, regardless of the mode of synthesis. It is anticipated that one skilled in the art of synthesizing biopolymers could make the peptide by using a modification of the chemical synthesis described below.
• the molecule can be made by direct synthesis, as described below. It is also contemplated that the molecule can be made by fluorination of the prolines in native collagen, either by enzymatic modifications of the immature collagen form (ProProGly)n or by substitution of the hydroxyl group in Hyp in mature collagen (ProHypGly)n with a fluorine atom.
• the success of the present invention relies on the superior electron-withdrawing ability of fluorine, relative to the hydroxyl group of hydroxyproline. It is therefore expected that a chemical modification that enhances the electron-withdrawing ability of the hydroxyl group (as opposed to replacing the hydroxyl group with a fluorine atom) will enhance collagen stability. It is anticipated that chemical modifications to the hydroxyl group of hydroxyproline that increase its electron-withdrawing ability would result in a collagen mimic with increased stability. Proposed chemical modifications of the hydroxyl group of hydroxyproline are described below.
• the collagen mimic was synthesized by a route based on tripeptide units of the form: FmocX-Y-GlyOH, where Fmoc is N ⁇ -9- fluorenylmethoxycarbonyl.
• Fmoc is N ⁇ -9- fluorenylmethoxycarbonyl.
• the placement of a glycine residue at the C-terminus of these units avoided problems caused by racemization (via azlactone formation) during the solid-phase coupling of activated peptide fragments.
• the tripeptide units were synthesized by using standard solution phase techniques (Bodanszky, 1994).
• the units were assembled with N ⁇ -tert-butyloxycarbonyl (Boc) rather than Fmoc protecting groups because Fmoc cannot withstand Pd/C-catalyzed hydrogenolysis that is necessary to deprotect the glycine residue.
• Boc N ⁇ -tert-butyloxycarbonyl
• reaction of BocFlpOSu with GlyOBn yielded a protected dipeptide.
• Removal of the Boc group in acidic dioxane followed by coupling with BocProOH gives a protected tripeptide.
• Removal of the benzoyl group by hydrogenolysis yields the Boc analog of 1, which was converted to 1 by removal of the Boc group and reaction with FmocOSu. All reagents used in the synthesis of the tripeptides are available commercially.
• a peptide that mimics single strands of collagen was synthesized by solid-phase coupling of tripeptide 1.
• each strand must contain at least 7 tripeptide repeats.
• a collagen mimic in which each strand contains 10 tripeptide units was synthesized. This 30-mer was synthesized on 2- chlorotrityl resin, which is amenable to solid-phase synthesis with Fmoc amino acids and allows for the cleavage of the polypeptide from the resin without sidechain or ⁇ - amino group deprotection, Fields and Noble, Int. ).
• 2- chlorotrityl resin which is amenable to solid-phase synthesis with Fmoc amino acids and allows for the cleavage of the polypeptide from the resin without sidechain or ⁇ - amino group deprotection, Fields and Noble, Int. ).
• Table 3 30-Mer peptides that mimic strands of collagen. Triple helices composed of units 2, 3, or 4 were used for thermodynamic measurements of collagen stability
• the triple-helical structure of collagen has a characteristic circular dichroism (CD) spectrum, with a peak signal at 225 nm.
• Figure 1 shows the CD spectrum of
• Each of the three collagen mimics has a strong signal at 225 nm, which is characteristic of the collagen triple helix.
• T m The melting temperature (T m ) of the helix formed by peptides 2 - 4 was determined by monitoring the CD signal at 225 nm as a function of temperature, according to the method of Long, et al., Biochemistry, 32:1 1688-1 1695, (1993).
• the chemical modification should: (1 ) make the hydroxyl group more electron withdrawing; (2) be small, so as not to interfere with the packing of triple helices against each other; (3) be uncharged, so as not to interfere with the packing of triple helices against each other.
• Potentially useful modifications include the addition of an acetyl group, a mesyl (methanesulfonyl) group, or a trifluoromethyl group to the hydroxyl group.
• the modification " reagent could be trifluoromethyl iodide.
• Each of these reagents could also modify other hydroxyl groups and amino groups on collagen. This may be detrimental to collagen stability. However, it is anticipated that the overall effect would be an increase in stability.

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• 1997
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